yes and that is extremely common, that doesn't count as colour blindness? what else would you call it.
Either way the "incomplete" forms of colour blindness are one of the most common forms of disability, so using color as the only distinguishing factor in consumer cable types is pretty exclusionary.
In attempting to defend Color blind people, you go too far in painting them as helpless. The use of color to distinguish thing is not in-and-of-itself exclusionary. Color blind people are still perfectly capable of distinguishing shades.
As long as you use fairly different shades of red and green, they can still match the cable to its matching color shaded port. Much UI accessibility is based on this fact.
Speaking as an only mildly colorblind person, I still tend not to use color to differentiate things. Even when it's two colors I can easily tell the difference between, I don't reach for color as a disambiguating feature unless I consciously try to.
Having to go even further than that and use shades of the colors I do have trouble with would be far more onerous.
Had you used a monochrome filter on software while adding accessibility you probably wouldn't suggest using shade as method of differentiation (it's simple to try, i recommend it). We already use luminescence mainly for discerning shape, when you throw "shades" into the mix it's usually too subtle for the purpose of differentiation.
Additionally in the physical world how are you going to determine the shade of something relative to something that is not present? i.e if you only have one cable in front of you. We don't have absolute perception, it tends to be affected by context, additionally the lighting now seriously affects your judgement... The reason this is so different to colour is because luminescence is a single receptor type (rods), with which you are trying to compare intensity of an area of one type of signal filled with other detailed information; whereas with colour you have three signal types (cones), in combination and at a lower detail than rods, so it's effectively separate information with at least 2^3 completely distinct permutations to differentiate in almost any lighting or context. This also explains why the absence of only a single cone receptor type has a significant impact on perception since it drops to 2^2 halfing the completely distinct permutations, of which two are merely black and white, so you actually drop from 6 to 2 non-monochromatic permutations - so you see it is far more challenging using either shade or partial cone types.
You use colors that the largest number of people can distinguish between.
At some point there will always be someone who something doesn't work for. You suggest using symbols, but what about people who are completely blind?
So you use something like a combination of color and braille, and then the rare person who is monochromatic can use the same solution as someone who is completely blind.
> At some point there will always be someone who something doesn't work for.
So your basically saying screw them all since it's impossible to include everyone? I just outlined for you the most common disability, it's particularly easy to avoid since they can still actually see.
> the rare person who is monochromatic can use the same solution as someone who is completely blind.
...how would you like to be told to learn brail in old age just cos your eyesight isn't quite good enough to read some small print?
No, that's just awful. Shape first, colour purely as an extra, then brail if the symbol is not relief or discernible enough, this is absolute basics of accessibility. This also helps everyone and functions in very low light since we all have low sensitivity to colour compared to luminescence, more so the older you get